This invention relates to the preparation of anhydrous magnesium chloride from its brines and hydrates.
In the electrolytic production of magnesium metal, molten, substantially anhydrous magnesium chloride is employed as the electrolyte. Magnesium chloride is very water soluble and crystallizes from solution as the hexahydrate, MgCl.sub.2 .6H.sub.2 O. Simple heating of the salt does not result in dehydration to the anhydrous form. Instead, Mg.sub.2 OCl.sub.2 and Mg(OH).sub.2 are produced together with HCl. Spray drying a hot saturated solution of magnesium chloride produces a product corresponding approximately to MgCl.sub.2 .2H.sub.2 O and having about 1% Mg(OH).sub.2 ; see U.S. Pat. 2,381,994.
Various methods have been prepared for producing anhydrous MgCl.sub.2. A number involve the chlorination of MgO or partially dehydrated MgCl.sub.2. One method produces essentially water-free magnesium chloride from the hexahydrate by thermal decomposition in a stream of hydrogen chloride gas. The presence of large quantities of corrosive hydrogen chloride and the necessity for maintaining essentially anhydrous conditions are obvious disadvantges.
Another method which the subject of a number of patents starts with ammonium carnallite and heats in two stages to drive off the water and then to fume off the NH.sub.4 Cl. One drawback is that the recovery and reuse of the NH.sub.4 Cl involves a sublimation step. Partial decomposition or hydrolysis of the ammonium chloride results in the formulation of corrosive HCl. In a large scale operation, this can present serious difficulties.
Pat. 2,381,994 shows heating a hydrous form of magnesium chloride with an alcohol to distill off the water and form solution of magnesium chloride from which anhydrous MgCl.sub.2 is recovered. Pat. 3,241,915 complexes hydrated MgCl.sub.2 with N,N dialkylamides and then decomposes the complex to recover the anhydrous salt. Pat. 3,471,250 shows complexing with various organic compounds containing S, O, P or N. However, these patents do not show the formation of MgCl.sub.2 from any magnesium oxides which may be present.
It is an object of this invention to produce essentially anhydrous magnesium chloride from magnesium chlorides hydrates and brines employing an amine hydrochloride complexing agent and decomposing the complex compound to produce the anhydrous salt.
A further object of this invention is to produce essentially anhydrous magnesium chloride from hydrates and brines containing magnesium oxides by reacting with amine hydrochlorides to convert the oxides to the chlorides, forming a complex compound and recovering essentially anhydrous magnesium chloride by thermal decomposition of the complex compound.
A further object of the invention is to employ as amine hydrochlorides in the process the hydrochloride salts of diethylamine, triethylamine, ethylenediamine, aniline, pyridine, toluidene or picoline.
Further objects will become apparent from the following specification and claims.